The data obtained from this exploratory grant will identify candidate genes activated or repressed by teratogenic and sub-teratogenic levels of retinoic acid (RA) in cranial neural crest. Subsets of these genes may be involved in cross talk between RA and growth factor/mitogen activated protein kinase (MAPK) signaling pathways. Retinoic acid, the active metabolite of vitamin A, may well be the most extensively studied developmental teratogen. While a great deal is known about how retinoic acid regulates gene expression, knowledge of what these gene products are and how they exert their effects in specific target tissues, lags behind. RA induced defects in animals and humans suggests the cranial neural crest is a target. The level of exposure further dictates the severity of the malformation. In preliminary studies, RA inhibited migration and proliferation of neural crest cells in culture in a dose dependent fashion. This inhibition was associated with loss of c-jun N- terminal kinase (JNK) phosphorylation, suggesting cross talk between RA signaling and JNK activation. The advent of functional genomics and microarray technology provides the opportunity to directly analyze the spectrum of genes expressed in target tissues, how expression patterns change over time following RA treatment, and how these changes might impinge on this and other signaling pathways. We hypothesize that the transcriptomes induced by high and low concentrations of RA in neural crest cultures treated over time overlap, but are not identical. Evaluation and comparison of these changes will allow us to (1) identify distinct sets of genes that may be critical teratogenic targets, (2) distinguish primary from secondary targets and determine how these might change relative to RA concentration, and finally (3) to identify changes in gene expression that impinge on MAPK signaling and affect biological processes associated with migration or proliferation. The use of a defined cell population where biological effects have been well characterized should facilitate identification of specific subsets of genes involved in mediating these processes. The specific aim is to examine the changes in the transcriptome of neural crest cultures following treatment with teratogenic and sub-teratogenic levels of RA. These changes will be evaluated over 48 hours in culture using gene chip microarrays to determine the time course of gene activation or repression. Cluster analysis will be used to analyze the expression patterns, to correlate these with specific gene families, and to determine how these families may impinge upon other signaling pathways within the neural crest that regulate migration and proliferation.